1. Field of the Invention
The invention relates to aircraft thrust reversers, and more particularly to a device for closing the shutters of such a thrust reverser and locking them in the closed position.
A thrust reverser forms a thin and substantially annular structure surrounding a turboshaft engine of the aircraft and centred on the geometric axis of the engine. More particularly, a thrust reverser comprises a fixed structure surrounding the engine and defining a plurality of radial apertures which can be closed or opened by movable shutters. When the shutters are closed, the function of the thrust reverser is to channel rearwards the flow of propulsion gases generated by the engine. When the shutters are open, the propulsion gases pass through the radial apertures and are diverted forwards, which diversion produces the thrust reversal.
2. Summary of the Prior Art
Each shutter is usually closed by at least one jack which is housed in the thickness of the reverser structure, one end of the jack being attached to the fixed structure, while its other end is attached to the shutter. The shutter is maintained in its closed position by at least one lock which is usually integral with the fixed structure. This lock comprises a movable latch which retains the shutter by means of a locking interface integral with the shutter. It will be noted that the lock instead may be integral with the shutter, and that in this case the locking interface will be integral with the fixed structure. The locking interface usually comprises a roller rotatably mounted at the end of a tie rod, and the latch of the lock acts on the roller to retain the shutter in its closed position.
When the jack is operated to close the shutter and the shutter approaches its closed position, the jack has to exert a substantial additional traction force in order to:
bring the shutter onto bearing surfaces ensuring precise positioning of the said shutter near the closed position, PA1 compress sealing gaskets which are generally of an elastomeric material and which are arranged between the periphery of the shutter and the fixed structure, PA1 trigger the lock of the shutter, which is usually of the passive type in that the latch of the lock is brought mechanically into the closed position by the movement of the locking interface which is carried by the shutter and which comes into engagement with the latch to move it into its closed position, the latch then locking itself automatically in the closed position by means of a spring and cam mechanism, PA1 "over-retract" the shutter, that is to say slightly overshoot the closed position of the shutter so as to allow automatic locking of the latch, the "over-retraction" temporarily entailing further compression of the sealing gaskets between the shutter and the fixed structure. This additional force requires strengthening of the jack, of the fixed structure and of the shutter, all of which increases the mass and cost of the thrust reverser.
Furthermore, the additional force has to be exerted under very unfavourable conditions in the case of thrust reversers of the well known type referred to as "pivoting-door" reversers. In such reversers, each radial aperture is shut off by a shutter, called a "door", which is pivotally mounted in the fixed structure so that the pivoting usually takes place in a plane including the geometric axis of the reverser. What happens, in this case, is that, when the shutter nears the closed position, the geometric axis of the jack approaches the geometric pivot axis of the shutter, such that the jack has to exert a very substantial additional force in order to produce only a reduced pivoting torque on the shutter.
Also, the additional force has to be further augmented in the case of reversers whose pivoting shutters are referred to as "self-opening". This is because the shutters in such thrust reversers tend to open naturally under the effect of the pressure of the propulsion gases generated by the turboshaft engine, this arising from the offset position of the pivots, and the jacks have to supply an additional force to overcome this tendency.
A first problem to be solved, therefore, is that of reducing the force required to be exerted by the jacks near the closed position of the shutters.
Another problem with known thrust reversers is that as soon as a shutter is closed and locked, its jack is disabled. The shutter is consequently relaxed and can start to vibrate or flap under the combined effect of the vibration transmitted from the engine to the reverser, and of the turbulent flow of the ambient air and of the propulsion gases at the ends of the shutter. This vibration or flapping of the shutter causes hammering and accelerated wear of the locking members, particularly the latch and the locking interface.
Thrust reversers with pivoting shutters are more exposed to this phenomenon because the forward ends of the shutters constitute leading edges exposed to the flow of ambient air or of the propulsion gases. The flapping occurs mainly at low engine speeds, when the pressure of the propulsion gases is insufficient to press the locking interface of the shutter against the latch of the lock.
Thus, a second problem to be solved by the invention is that of reducing, or even suppressing, the vibration and flapping of the shutters in the locked position.